Revealing the stimulus-driven component of attention through modulations of auditory salience by timbre attributes

Attention allows a listener to select the relevant information of the environment and to ignore others. But irrelevant stimuli sometimes manage to capture it and stand out from a scene because of bottom-up processes driven by salient stimuli. This attentional capture effect was observed using an implicit approach based on the additional singleton paradigm. In the auditory domain, it was shown that attributes of sounds such as intensity and frequency tend to capture attention during auditory search (cost to performance) for targets defined on a different dimension such as duration. In the present study, the authors examine whether a similar phenomenon occurs for attributes of timbre such as brightness (related to the spectral centroid) and roughness (related the amplitude modulation depth). More specifically, the relationship between the variations of these attributes and the magnitude of the attentional capture effect was revealed. In experiment 1, the occurrence of a brighter sound (higher spectral centroid) embedded in sequences of successive tones produced significant search costs. In experiments 2 and 3, different values of brightness on one hand, and different values of roughness on the other hand confirmed that attention capture is monotonically driven by the sound features. In experiment 4, the effect was found to be symmetrical; the same positive or negative difference in brightness produced the same cost to performance. Experiment 5 revealed the non-additivity of the effect produced by variations of the two attributes. This work provides a methodology for quantifying the bottom-up component of attention and brings new insights on attention capture and auditory salience.